A related art mobile communications system which handles IP packets is disclosed by, for example, “Trends in standardization of mobile communications protocols for the Internet” (Institute of Electronics, Information and Communication Engineers paper magazine 2001/10).
According to Mobile IPv6, every time a mobile node moves, a binding response for updating of binding is exchanged between the mobile node and a home agent. Therefore, when the mobile node moves frequently, such control traffic causes congestions of the network.
Furthermore, when it takes much time for the mobile communications system to carry out binding with a home agent or a communications-partner node, packets are relayed to a location where the mobile node stayed previously and this causes a loss of some of them.
In order to solve such a problem, hierarchical mobile IPv6 and cellular IPv6 are proposed, for example.
In related art mobile communications systems which handle IP packets, even in a case of hierarchical mobile IPv6 or cellular IPv6, an SPF (single point of failure) problem arises in a local home agent and a boundary router which serves as a cellular IP gateway. A problem with related art mobile communications systems is therefore that it is difficult to thoroughly eliminate the possibility that there causes congestions of the network due to increases in the amount of control traffic when a mobile node move frequently, or there causes a loss of packets because the packets are relayed to a location where the mobile node stayed previously when it takes much time to carry out updating of binding and route changing due to the movement of the mobile node.
Another problem with mobile communications systems which assign high-speed downlink packets, such as HSDPA (High-Speed Downlink Packet Access), to two or more communications nodes at a high speed is that when a mobile node moves from a cell under control of an arbitrary base transceiver station to a cell under control of another arbitrary base transceiver station and performs a handover using, for example, SSDT (Site Selection Diversity Transmit Power Control) which minimizes downlink interference power at this time, a control delay occurs due to control of transmission via radio downlinks extending from an RNC to both the source base transceiver station from which the mobile node is moving and the destination base transceiver station to which the mobile node is moving, or when both the source base transceiver station and the destination base transceiver station receive primary cell/non-primary cell control data from the mobile node via radio uplinks, as in the case of using SSDT, there causes congestions in the network since the RNC transmits downlink data packets, via the network, to both the source base transceiver station and the destination base transceiver station.
A further problem with mobile communications systems which assign high-speed downlink packets, such as HSDPA, to two or more communications nodes at a high speed is that when base transceiver stations are so constructed as to carry out ARQ (Auto Repeat reQuest), all base transceiver stations which are carrying out communications with the mobile node need a memory space for temporary buffering of packets to be resent.
A still further problem is that even in a case of providing multiple values of transmission symbol in space by simultaneously transmitting plural different transmission symbols from a plurality of transmit antennas using an MIMO (Multi-Input Multi-Output) transmission method, so as to implement further high-speed packet communications, the implementation of this technique in each base transceiver station causes an increase in the cost of each base transceiver station because of increases in the number of transmitters and the number of antennas included in each base transceiver station, while the system cannot obtain optimal cost performance since mobile nodes can require different data speeds.
The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a radio communications system which, when a routing function is provided to each base transceiver station and a mobile node is moving from a cell under control of an arbitrary base transceiver station having the routing function to another cell under control of another arbitrary base transceiver station having the routing function, can reduce the frequency of generation of control packets for updating of binding and route changing, which are to be transmitted to a boundary router, and can improve network congestions and losses of packets since the radio communications system can localize congestions of packets on the network due to the movement of the mobile node only between the source base transceiver station from which the mobile node is moving and the destination base transceiver station to which the mobile node is moving by controlling the destination base transceiver station or the mobile node to transfer packets from a communications-partner node to the destination base transceiver station.
It is another object of the present invention to provide a mobile communications system which assigns high-speed downlink packets, such as HSDPA, to two or more communication nodes at a high speed, and in which, when a mobile node is moving from a cell under control of an arbitrary base transceiver station to another cell under control of another arbitrary base transceiver station and performs a handover using SSDT which minimizes downlink interference power at this time, the source base transceiver station transfers downlink packets to the destination base transceiver station using a routing function thereof, each of the source base transceiver station and destination base transceiver station has a function of detecting information transmitted from the mobile node and indicating whether or not the local station is a base transceiver station for downlink radiocommunications, and the source base transceiver station has a function of determining and selecting whether or not to transmit the downlink packets, via a network, to the destination base transceiver station based on the detection result, so that the source base transceiver station and destination base transceiver station can implement a handover function, which is conventionally performed by an RNC, thereby preventing the occurrence of network congestions which conventionally occur due to transmission of packets to both the source base transceiver station and the destination base transceiver station at the time of a soft handover, reducing a control delay, implementing a handover which is suitable for the conditions of a radio link with the mobile node, which vary with time, and which enables a quick cell selection, and hence improving a maximum throughput via the radio downlink.
It is a further object of the present invention to reduce the cost of each base transceiver station in the mobile communications system which assigns high-speed downlink packets, such as HSDPA, to two or more communication nodes at a high speed, by making it possible for only a base transceiver station with which the mobile node has established a radio link connection for the first time to perform a function of temporarily buffering packets to be resent to the mobile node, which causes a problem when each base transceiver station can perform ARQ, by performing a function of transferring packets between base transceiver stations using the routing function.
It is a still further object of the present invention to implement MIMO transmission with good cost performance, by, when simultaneously transmitting a plurality of different transmission symbols from a plurality of transmission antennas to provide multiple values of transmission symbol in space according to an MIMO transmission method, thereby implementing higher-speed packet communications, selecting a number of base transceiver stations according to data speed requested by the mobile node from two or more base transceiver stations providing cells adjacent to the cell in which the mobile node is staying, dividing each downlink packet into plural parts for the selected base transceiver stations, and transferring the plural parts to the selected base transceiver stations, respectively, using the routing function.